The king of improv feature films, Christopher Guest, is coming to HBO this May with Family Tree. The new comedy series stars Chris O’Dowd, who you might know from Bridesmaids or Girls, as a man who “gets a box of treasures” and becomes obsessed with his family’s history.

In our spring preview issue, Guest told EW that each episode has an eight-page outline and the rest is improv. “But we’ve written a huge back history for every character, which took us six or eight months to come up with,” Guest explained. “We’ve done an entire family tree going back to the 1700s.”